Cloutier, et al, U.S. patent application Ser. No. 11/596,836 entitled Honing Feed System Having Full Control of Feed Force, Rate and Position, now U.S. Pat. No. 7,371,149, is incorporated herein by reference in its entirety. The disclosure of Cloutier, et al, U.S. Provisional Application No. 60/842,321, filed Sep. 5, 2006, is also incorporated herein by reference in its entirety.
Currently some new models of honing machines available from Sunnen Products Company are using a feed force sensing device to improve the control and results of the honing process. This technology is described in detail in the above-referenced pending U.S. and international patent applications, Cloutier, et al, Honing Feed System Having Full Control of Feed Force, Rate and Position.
Essentially, according to the present invention, the type of feed system described in the above-referenced pending patent application, and other feed systems with force sensing capability, can be used in conjunction with the honing tool itself to produce reliable pre- and post-processing gaging of the finished bore, or hole, herein interchangeably referred to by the term bore. Furthermore the data gathered and processed by the machine control computer during this step can be used to make accurate compensations for abrasive wear of the honing tool.
Current bore measuring methods can be generally categorized as post-process methods and in-process methods. The in-process methods primarily consist of either a plug gage that tries to enter the bore during the process or an air gage probe, either separate or built into the tool, measuring the bore during the process. Post-process gaging can vary in sophistication from manually placing a bore gage in the bore to automated air gage probes that enter the bore and take multiple readings. No known methods exist where the tool itself, lacking any dedicated measuring attachment, is used to measure the size of the finished bore.
In the past, most honing feed systems did not have the ability to accurately measure both feed force and feed position. Since the elements of the feed system and honing tool are not perfectly rigid and exhibit some degree of elasticity, it is impractical to attempt to use the honing feed system as a bore measuring system unless both force and position can be measured accurately.
One example of prior art, does combine both force and position measurement. European Patent No. EP 0 575 657 B1 (Grimm, et al, Method and Machine for Finishing a Bore in a Work Piece) uses a feed force measuring device, for determining a target end point (final encoder position) before the honing process begins. This method uses a calibration ring (or sample workpiece) that has been made with a bore size equal to the desired final bore size. The honing tool is expanded in the bore of this calibration ring until a certain level of force is measured in the feed force measuring device. To minimize errors arising from tool and feed system elasticity, the last recorded feed force of the last honing cycle is used. When this force is reached with the tool in the calibration ring, the feed system position is recorded as the target position for the next honing cycle.
An observed shortcoming of the above-discussed disclosure of Grimm et al., however, is that no post-process measurements of the honed bore are made to verify the achievement of the desired bore size. Thus, no capability is provided for the machine control system to gather accurate process data for purposes such as improving the accuracy of the honing process.
Another observed shortcoming in the disclosure of Grimm et al., is that no difference between measurements made under static and dynamic conditions is noted or recognized. In Grimm et al., in the calibration ring, the feed force and position are measured under static conditions, that is with no relative rotation and/or stroking of the tool and workpiece, but, in the workpiece bore, the measurements are made under the dynamic conditions of the honing process, i.e., the honing tool is at least rotating and there may be a relative stroking motion between the tool and the bore. Experience has shown that forces and positions recorded under dynamic conditions will not exactly result in the same bore measurement as when the same level of force is applied under static conditions.
Still further, in the Grimm et al. disclosure, compensation for tool wear is made periodically, based on differences between feed position measurements taken in the calibration ring before and after at least one workpiece has been honed, and thus, as another shortcoming, the compensation is not applied to the immediately affected workpiece or workpieces, but instead, to subsequently honed workpieces.
Accordingly, what is sought is a capability of making pre- and post-process measurements of bores of honed workpieces, that verify the desired bore size and allow the ability for the machine control system to gather accurate process data for purposes including improving the accuracy of the honing process and compensation for tool wear.